On-load tap changer for transformers



Patented Mar. 16, 1954 UNITED STATES PATENT OFFICE ON-LOAD TAP CHANGER yEOE TRANSFORMERS Application October 4, 1951, Serial No. 249,695

Claims priority, application Sweden December 2, 1950V 2 Claims. l

On-load tap changers for transformers have for their object to perform a change-over of a terminal or" a winding from one tap to another in the same winding or in a separate regulating winding in rsuch a manner that the load current can flow through the transformer without interruption at any time during a tap change. In order to obtain such an interruption-free tap change without short-circuiting the parts of the winding which are between adjacent taps, the change-over from one tap to another is made in two steps by means of two alternately acting contacts, one of which first connects the terminal to a succeeding tap over an impedance, the direct connection then being made by means of the other contact.

In order to attain a larger regulating range hy means of a given regulating winding, the `tap changer may be provided with a switch by means of which the parts of the regulating winding are successively disconnected and then again successively connected in, but in the opposite direction.

The present invention concerns an arrangement in tap changers either for actuating the said alternately acting Ycontacts of the said switch,

or for actuating yboth the'contacts and the switch, by means of a driving member running with a substantially constant speed, for instance a directly coupled motor or a iiywheel with stored energy, and in such a manner that the contacts are moved practically momentarily from one contactposition to another and remain in this position until the time comes for removal to the next contact position.

Hitherto it has only been possible to attain such a motion by means of a very complicated intermittently acting mechanism. By the present invention, however, the desired motion oi the contacts of the tap changer is attained by means of simple and reliable elements and a driving member running with a practically constant speed. The invention is chiefly characterised in that between the driving member and the contacts oi the tap changer there is inserted a toothed gear train which comprises at least three seriesconnected non-circular, for instance elliptical, toothed wheels. According to one form of the invention, the gear mechanism may comprise two parallel trains of wheels, which are driven from a common pinion driven by the driving member,

which trains each drive one of the contacts of the tap changer, and according to another form of the invention, this gear mechanism may comprise a third wheel train, driving the said switch.

It has previously been proposed to use ellipti- (Cl. S23-43.5)

cal toothed wheels in order to attain a varying gear ratio. In hitherto known gears, however, only one pair of elliptical wheels has been used, and the change of the ratio obtainable in such a pair has therefore been rather limited. 'The present invention, however, concerns the use in each gear train of at least three noncircular toothed wheels in series, and therefore any desired variation of the gear ratio can be attained. For the present purpose this is of the greatest importance, .because it is possible to attain, in combination with a continuously rotating driving shaft, a stepbystep motion of the contacts and also a practicallyk momentary motion of the switch, which occurs first when another contact or switch has performed a plurality of motions.

On the accompanying drawing the invention is shown applied to a tap changer of the type comprising a switch for connecting a regulating winding either in the same direction as the main winding or in the opposite direction, and with a resistor as current-limiting impedance.

In the drawing, 2 designates a drivingr shaft which is connected with a continuously moving driving member, for example a motor, not shown in the drawing. An elliptical pinion .3 mounted on shaft 2 engages two elliptical toothed wheels 4' and l, which in turn engage elliptical toothed wheels 5' and 5, which are secured to the partially screw-threaded shafts 6', 6", respectively. On the threaded parts of these shafts, nuts i and T" are mounted, which are mechanically, but not electrically, connected with contacts 8 and 8" respectively. These contacts slide on contact bars Il and Ii", and during their motion along lthese bars are brought into contact with tap contacts iti- M9 and iti-M9, respectively. These tap contacts, other than contacts and |55, are connected with taps on parts ini-HB4 of the regulating winding it. Tap contacts M5 and |55 are connected to one end of the main winding 9. The contact bar i i is directly connected with the line terminal l2 to the transformer, whereas the contact bar Il is connected with line terminal l2 through a resistance i3.

i pinion 2l is also mounted on the shaft 2 and engages an intermediary wheel 22. On the shaft of this latter wheel there is an elliptical pinion 23 which engages a non-circular toothed wheel 24. On the shaft of the latter wheel, there is an elliptical pinion 25, which acts over an intermediary elliptical toothed wheel 2S on an elliptical toothed wheel 2 on a partially screw-threaded shaft Il. On the threaded part of this shaft a nut I6 is mounted which is mechanically, but not electrically, connected with a contact i9 sliding on a contact bar 28, and is alternately brought into contact with the contacts I9 and 20. The contact bar 28 is directly connected with the main winding 9 of the transformer, the contact I9 is connected with one end of the regulating winding I0, and the contact 20 is connected With the other end of said Winding.

The arrangement acts in the following way: In the position of the contacts 8' and 8", shown on the drawing, the line terminal I2 of the transformer is connected to the main winding 9 of the transformer over the part |01 of the regulating winding I0. When the driving shaft 2 is in motion in such a direction that the contacts 8' and 8" are moved downwards, the nut 1" is first moved downwards one step, so that the line terminal I2 is connected with tap contact |51 through the resistance I3, and so that the two parts |01 and |02 of the regulating winding are connected in series with the main winding through the resistance I3. The contact 8' then performs a rapid movement down to tap contact |41, and during this motion the contact 8 remains at rest on tap contact |57. In this manner the contacts 8 and 8" alternately step downwards until at last all four parts of the regulating winding have been connected in series with the main winding. The tap changer has now reached one of its end positions. driven in the opposite direction, the different parts of the regulating winding are successively disconnected until the contacts 8 and 8" reach tap contacts |45 and |55, respectively, in which position the whole regulating winding is out of circuit. When the contact 8" reaches tap contact I 54, the line terminal I2 is connected to the winding 9 through the resistance I3 over tap contact |54, tap contact |58, part |04 of the regulating winding, contact 20, contact I8, and bar 2B. As will be seen, a fourth part of the regulating winding is connected to the main winding, but now in opposite direction, and upon continued motion upwards of the contacts 8' and 9 the different parts of the regulating winding again are connected into circuit in series with the main winding 9, but now, as said before, in opposite direction. The movement of the contact I8 from contact I9 to contact 20 is performed during the period between contact 9' leaving tap contact |46 and contact 8" arriving at tap contact |54, for the reason that during this period the contact I8 is entirely out of action, as contacts |45 and |55 are directly connected to the main winding 9.

The movement of the contact I8 from one position to the other takes piace only once during the time necessary for moving the contacts 8 and 8" from the lowermost to the uppermost position or vice versa, and this is made possible by the large gear ratio, and the large variation of the gear ratio, which are attained by the use of non-circular toothed wheels connected in series between the pinion 2| and the toothed wheel 21.

The invention is notlimited to the form shown on the drawing but comprises all arrangements where the movement of a contact in a tap changer is performed by means of a toothed wheel train comprising at least three non-circular toothed wheels. It is not, of course, necessary that the motion of the contacts takes place along a straight line, because a circularmotion of the contacts can also be used.

I claim as my invention:

1. Gear mechanism for the tap changers of a transformer with two moving contacts, comprising a driving member rotating at uniform speed, a non-circular tooth gear wheel driven by said member, two non-circular idler tooth wheels both meshing with and driven by the rst-mentioned wheel, a non-circular tooth Wheel meshing with and driven by each of said idler wheels, and means whereby intermittent motion of the wheels driven by said idler wheels is transmitted to said contacts to move them with a step-by-step motion.

2. Gear mechanism for the tap changers of a transformer with two moving contacts, comprising a switch for reversing a regulating winding in relation to a main transformer winding, a driving member rotating at uniform speed, a gear train having at least two non-circular tooth wheels for imparting intermittent motion to said switch from said member, two trains each having at least three non-circular tooth wheels for imparting intermittent motion to said moving contacts over the tap contacts of the winding, the first-mentioned gear train providing a large gear ratio in relation to the other gear trains so that the tap changer and the switch will effeet only one switch-over during the time the contacts of the tap changer move over all the tap contacts.

UNO OLSSON.

References Cited in the ille of this patent UNITED STATES PATENTS Number Name Date 2,325,936 Blume Aug. 3, 1943 2,551,943 Gulow May 8, 1951 

